The information on this page is to help you if you are having problems sending mail to Oxford users.

Receiving a bounce

550 Mail transactions must start with EHLO/HELO

RFC2821 s4.1.1.1 

a client MUST issue HELO or EHLO before starting a mail transaction

Configure your server to use the EHLO or HELO command before MAIL.

550 Invalid HELO (foo) used by 192.168.4.90

RFC1123 s5.2.5 

The sender-SMTP MUST ensure that the <domain> parameter in a HELO
command is a valid principal host domain name for the client host

RFC2821 s4.1.1.1 

The argument field contains the fully-qualified domain name of the SMTP
client if one is available.  In situations in which the SMTP client
system does not have a meaningful domain name (e.g., when its address is
dynamically allocated and no reverse mapping record is available), the
client SHOULD send an address literal (see section 4.1.3), optionally
followed by information that will help to identify the client system.

Configure your server to give either its Fully-Qualified Domain Name or IP address literal as the argument to the EHLO or HELO command.

550 Verification failed for <user@i-made-this-up-just-now.com>

The sender domain must exist and have valid DNS records.

Not receiving a bounce

It is possible the Oxford user has filtered your message into their junk-mail box. Ask the user to check, and add your sender address to their whitelist if appropriate.